Think having a baby is a drain on your time? An octopus mother brooded her eggs for four and a half years – the longest brooding period of any known animal.

Egg-laying animals brood to protect their eggs from potential predators, ensuring they hatch successfully. Female octopuses also regularly blow water on their eggs to bathe them in the oxygen they need to survive.

Bruce Robison and his colleagues at the Monterey Bay Aquarium Research Institute in California were surveying deep-sea animals in 2007 when they spotted a female octopus in a submarine canyon at the centre of Monterey Bay in the Pacific Ocean (pictured). The octopus, a member of the species Graneledone boreopacifica, was clinging to a rocky ledge some 1400 metres down, protecting a brood of 160 eggs, each the size of a small olive.

Over the following four and a half years, the team returned to the site 18 times. On every visit, the group found the same octopus – identified by her distinctive scars – in the same location. Finally, on a visit in 2011, one month after their last visit, the researchers found only the remnants of hatched egg capsules.

The marathon brood was no easy ride. As the octopus's translucent eggs grew larger, she gradually lost weight, and her skin became loose and pale. Robison's team noticed that the animal paid little attention to passing prey.

"It's not impossible that she fed at some point during her brood, but it's not characteristic of any known octopus species to do so, and we have never observed unattended octopus eggs," says Robison. The brisk 3 °C water may have helped the octopus survive by slowing her metabolism and energy requirements.

But ultimately the octopus will have sacrificed her life for her brood. Reproduction is the final stage of life for all female octopuses, says Janet Voight at the Field Museum in Chicago. During this stage, their bodies change to direct their energy to producing and caring for eggs.

"In extreme habitats like the deep ocean, which is harsh and demanding, animals have two reproductive options: one is to make a million eggs and send them on their way, and the other is to produce just a few eggs and make every effort to ensure their success," says Robison.

This evolutionary strategy appears to have worked well for G. boreopacifica, which is one of the most abundant and long-lived species of deep-sea octopus in the north-east Pacific Ocean.

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